The water felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a well known commercial process for manufacturing acoustical ceiling tile or panels. In this process, aqueous slurry of mineral wool, lightweight aggregate, cellulose fiber, binder and other desired ingredients is flowed onto a moving foraminous support wire, such as that of a Fourdinier or Oliver mat forming machine, for dewatering. The slurry may be first dewatered by gravity and then dewatered by vacuum suction means to form a base mat. The wet base mat is then pressed (with or without the application of additional vacuum) to the desired thickness between rolls and a support wire to remove additional water. The wet base mat is dried in heated convection drying ovens and the dried material is cut to the desired dimensions, fissured and/or perforated to impart acoustical absorbency and optionally top coated, such as with paint, to produce acoustical tiles and panels.
Mineral wool acoustical tiles are necessarily very porous to provide good sound absorption. As taught in U.S. Pat. Nos. 3,498,404; 5,047,120 and 5,558,710, all incorporated herein by reference in their entirety, mineral wool fibers have also been incorporated into the composition to improve sound absorption properties and to provide lightweight acoustical tiles or panels.
U.S. Pat. No. 5,964,934, incorporated herein by reference in its entirety, teaches the use of an expanded perlite, treated with a silicone compound to reduce its water retention, in a furnish of mineral wool, expanded perlite, cellulose fiber, and optionally a secondary binder in a water-felting process to produce an acoustical tile product.
Acoustical tile composition must contain a binder, which has typically employed starch. U.S. Pat. Nos. 5,911,818 and 5,964,934, incorporated herein by reference in their entirety, suggest that as much as 15% by weight of the composition may be starch although 6-7% by weight is more normally used.
U.S. Pat. No. 5,250,153, incorporated herein by reference in its entirety, describes the use of latex binders for acoustical tile compositions and a wide variety of latex binders have been suggested for this use.
U.S. Pat. No. 6,855,753, incorporated herein by reference in its entirety, has suggested that a wet-strength resin such as a polyamine epichlorohydrin resin be used to replace conventional starch binder and that the resulting composition may be more efficiently fabricated into acoustical tiles and panels in a water felting process.
US Patent Application Publication Number 2004/209071 A1, incorporated herein by reference in its entirety, discloses a composition for slurry for manufacture of acoustical panels includes one or more fillers, one or more binders, and water and zinc pyrithione.
US Patent Application Publication Number 2005191465 A1, incorporated herein by reference in its entirety, discloses an abuse-resistant, cast acoustical ceiling tile having improved impact resistance and excellent sound absorption values. The ceiling tiles have aggregate particles applied to the surface of a wet pulp in the casting process and the particles are embedded in the pulp by compression with a roll and/or smoothing plates.
A CONSTELLATION brand base mat is a sag-resistant, lightweight mineral panel produced on a foraminous support wire by forming a dilute aqueous dispersion of mineral fiber, an anionically stabilized latex binder and a binder, coupling the binder solids onto the mineral fiber materials by adding a small amount of a flocculant such as through the use of a cationic polyacrylamide, and passing the slurry onto a first flooded section of the support wire to form an open, entangled, structural mass having water in interstitial spaces of the entangled mass. Water is stripped from the mass and the mass dried by passing heated dry air through the open entangled structure.
MARS CLIMAPLUS® brand acoustical panel produced by USG Interiors, Inc. is a high-end acoustical ceiling product utilizing a back-coated CONSTELLATION base mat and a laminated non-woven fiberglass scrim facer. The MARS brand product has many advantages, including a smooth white texture, excellent high-humidity sag performance, good acoustical value, high recycled content, low formaldehyde emissions, and antimicrobial properties. The current MARS brand product is ¾″ (1.91 cm) thick with a NRC of 0.70 and a ceiling attenuation class (hereinafter also referred as “CAC”) of 35.
Noise reduction coefficient (NRC) is a scale representation of the amount of sound energy absorbed upon striking a particular surface, with a NRC value of 0 indicating perfect reflection and a NRC of 1 representing perfect absorption of sound energy. The NRC value is an average of four sound absorption coefficients of the particular surface at frequencies of 250 HZ, 500 HZ, 1000 HZ and 2000 HZ, which cover the range of typical human speech. In laboratory test of materials in a laboratory per ASTM C423, only the face of the sample is exposed to the sound energy, as would be the case in a typical installation. Under some circumstances NRC's greater than 1 may be obtained, but this is an artifact of the test method due to diffraction/edge to area effects.
The Ceiling Attenuation Class (CAC) rating quantifies how much sound is lost when it is transmitted through the ceiling of one room into an adjacent room through a common plenum. A higher CAC rating indicates that the ceiling system allows less sound transmission. The CAC is measured using the test standard ASTM E 1414, in which the sound levels are measured in the source room and an adjacent room.
The Normal Incident Sound Absorption can be determined in accordance with a modified ASTM E1050-98, in which the Normal Incident Sound Absorption is measured in an impedance tube from the average of four frequencies, i.e., 250, 500, 1000 and 1600 Hz. The ASTM E 1050-98 is “modified” because the fourth frequency is 1600 Hz, not 2000 Hz. The sample is tested without a backing air space, i.e., with the acoustical panel resting on a flat metal surface, on a Brüel & Klaer Pulse™ Material testing system consisting of Pulse™ Material testing Program Type 7758, Two-microphone Impedance Measurement Tube Type 4206 (400 mm diameter), Power Amplifier Type 2706 and Pulse™, the Multi-analyzer System Type 3560. The ENRC value is often used as a measure of the acoustical absorption properties of a lab sample.
A higher NRC product with the advantages of the current MARS CLIMAPLUS® brand acoustical panel product would be desirable.
There have also been attempts to produce a higher noise reduction coefficient (NRC) Constellation product using the water felting process by lowering the stock flow of the composition in an attempt to produce a lower density product, but these attempts only produced a product that had a comparative density to conventional panels but at a reduced product thickness.